Preparation of lactic acid



e Other objects of the invention will in 2,847,464 Patented Aug. 12, 1958 United States Patent Ne e dha'm, Mass., assignors, by mesue assi nments, to EscambiaChem'ical Corporation, Pace, Fla., a corpo- No-Drawing; 'Application'December 29, 1955 Serial No. 556,067

3 Claims. (Cl.260'533) Ihisfinvention relates'to the-production of valuable che'micals and inparticular to the production of alpha hydroxy carboxylic acids and derivatives thereof.

A pi incipal object of the present invention is to provide an economical .processfor making lactic acid from propylene:

j Another object of the invention is to provide a process for converting propylene to esters of lactic acid.

Still another object of the invention is to provide an 7 integrated, economical process for making acrylic acid and esters thereof from propylene.

I part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process in- "volvingthe severalsteps and the relation and the order of one ormore of such steps with respect to each of the others. which are exemplified in the following detailed dis- "closure; and the scope of the application of which will beiiidicf'ated in the claims- "For'afuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

A particular aspect of the present invention is directed to the conversion of organic compounds containing at i least 'onealpha olefinic linkage tothe corresponding alpha hy'tlro'xy":carboxylic acid. This is preferably achieved b'y co'ntacting a preferredorganic compound with an oxidizing medium containing an oxidizing agent selected from the group consisting of dinitrogen tetroxide, dinitrogen trioxide and mixtures thereof, and reacting the resultant; reaction products with'nitric acid. The resultant alpha hydroxy carboxylic acid may subsequently be dehydrated or esterified or subjected to an esterification and a dehydrationa In. one preferred embodiment of the inventiom'propylene is converted to lactic acid. The resultant lactic acid may subsequently be dehydrated or esterified or subjected to both an esterification and a dehydration to produce acrylic acid and suitable esters thereof.

The reaction between propylene and an oxidizing medium containing an oxidizing agent selected from the group consisting of dinitrogen tetroxide, dinitrogen trioxide and mixtures thereof preferably takes place when there is present in the oxidizing medium at least one mole of oxidizing agent per mole of propylene to be converted. This initial reaction is preferably carried out at relatively =T1ow temperatures and in particular at temperatures below about 40 C.

The reaction between the reaction products resulting from the above initial reaction and nitric acid is also carried out at temperatures below about 40 C. The quantity of nitric acid employed is preferably based on the quantity of propylene to be converted. Thus it is preferred that there be present for this second reaction at least one mole of nitric acid for each mole of propylene originally reacted. In one preferred embodiment of the invention, the preferred quantity of nitric acid is present in the oxidizing medium so that the reaction products resulting from An acid charge comprised of 58.3 percent by weight of percent nitric acid, 16.7 percent by weight of dinitrogen tetroxide and 25.0 percent by Weight of water was pumped into a stirred stainless steel reactor at a rate of 9.3 grams per minute. Simultaneously a stream of propylene was bubbled into the liquid in the reactor at a rate of about 0.031 gram of propylene per gram of acid charge. The liquid holdup in the'reactor was held constant by means of an overflow device. A coolant circulating throughthe-jacket of the reactor served to hold the temperature constant at about 15 C. The flows were continued until the composition of the effluent solution remained constant with respect to time and then long enough to allow a sample to be collected. A total of about 595 grams of acid charge and about 18.4 grams of propylene were charged to the reactor during the sample collection period.

The sample withdrawn from the reactor was distilled at room temperature to remove the nitric acid and nitrogen oxides. The residue was treated with 280 cc. of a 2 N aqueous solution of sodium hydroxide at 60 C. After acidification and ether extraction of the saponification mixture, evaporation of the ether led to an oily product. The oil was dissolved in water and suflicient calcium carbonate was added to the solution to bring the pH thereof up toabout 5. The resultant calcium lactate acid is believed to take place in a series of steps. The

mechanism of this reaction consists of an initial or first step wherein propylene reacts 'with an oxidizing agent such as dinitrogen tetroxide, dinitrogen trioxide or a mixture' of both at a relatively low temperature to form nitrogen-containing propylene products; These nitrogen-containing propylene products react with nitric acid to produce the alpha hydroxy carboxylic acid, i. e., lactic acid. Thus the reaction may be carried out in one step or stage by having the preferred quantity of nitric acid present with the oxidizing agent in one medium so that the intermediate nitrogen-containing propylene products from the propylene and oxidizing agent reaction immediately react with the nitric acid. The reaction may also be carried out in two steps by omitting nitric acid from the initial oxidizing medium and subsequently adding the intermediate nitrogen-containing propylene products formed to nitric acid.

The oxidizing medium may contain only an oxidizing agent selected from the group consisting of dinitrogen tetroxide, dinitrogen trioxide and mixtures thereof, or it may contain a mixture of the oxidizing agent and nitric acid. The oxidizing medium preferably contains at least one mole of oxidizing agent per mole of propylene which is to be converted.

With regard to the use of dinitrogen tetroxide, it should be noted that dinitrogen tetroxide is an equilibrium of the monomer (N0 and the dimer (N 0 The equilibrium concentration of the monomer is a function of the temperature, as described in Inorganic Chemistry,

3 F. Ephraim, 3rd English Edition, New York, Nordman, 1939, page 667. When used in the specification and the claims, the expression dinitrogen tetroxide is intended to include the equilibrium concentration of the monomer at the temperature employed.

The nitric acid, it not present in the oxidizing medium, is subsequently added to the reaction products of the first reaction or, preferably, the reaction products are added to it. Nitric acid with an HNO concentration of from 25 percent to 100 percent by weight and particularly with an HNO concentration above about 50 percent by weight is suitable for the reaction. The quantity of nitric acid employed is preferably based on the quantity of propylene initially reacted. It is thus preferred that there be employed at least one mole of nitric acid for each mole of propylene originally reacted. The nitric acid need not be added as such but may be formed in the reaction mixture. For example, it may be formed by the reaction of added water with dinitrogen tetroxide. As used in the specification and claims, nitric acid will refer not only to aqueous solutions having an I-INO concentration above 25 percent by weight but also to 100 percent nitric acid.

The over-all reaction is preferably carried out at temperatures below about 40 C. When the oxidizing medium contains both nitric acid and an oxidizing agent so that the over-all oxidation will occur as one operation, temperatures below about C. are desirable. When the reaction is carried out in two separate steps, the initial Y reaction is preferably carried out at temperatures below about 10 C. while the second reaction employing nitric acid may be carried out at temperatures between about C. and 40 C.

The structure of the products resulting directly from the reaction of propylene and a preferred oxidizing agent is not known with absolute certainty. However, reaction of these products with nitric acid results in products such as the desired lactic acid and nitrate esters of lactic acid; these latter compounds are capable of being easily converted to the desired lactic acid. Thus, in some instances, a portion of the desired lactic acid is obtained after a suitable hydrolysis. I

The lactic acid obtained may be subsequently esterified or dehydrated or subjected to both an esterification and a dehydration. If esters of lactic acid are desired, then the lactic acid can be simply esterified with a suitable alcohol such as the aliphatic alcohols, methanol, ethanol, propanol, the butanols and the like. Such esters may be produced by the general procedure described by Clinton and Laskowski, Journal of American Chemical Society 70, 3135 (1948) or in U. S. Patents 1, 775,636, 2,336,317

4 and 2,348,710. If acrylic acid is the desired end product, then the lactic acid can be simply dehydrated. Likewise, if an ester of acrylic acid is desired, then the lactic acid may be esterified with a suitable alcohol and the ester dehydrated. The dehydration may be accomplished by means of P 0 or by any of the procedures shown in British Patent 409,733 or U. S. Patents 1,993,089, 2,054,242, 2,100,993, 2,184,934, 2,226,645, 2,244,389 and 2,356,247.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. The process which comprises contacting propylene with an oxidizing medium ata temperature below about 40 C., said oxidizing medium containing at least one mole of nitric acid and at least one mole of dinitrogen tetroxide for each mole of propylene employed, said nitric acid having an HNO concentration in excess of about 25 percent by weight, subjecting the resultant reaction products to hydrolysis conditions, and recovering a preponderance of lactic acid.

2. The process of claim 1 wherein said nitric acid has an HNO concentration in excess of about percent by weight.

3. The process of forming lactic acid which comprises contacting propylene with dinitrogen tetroxide at a temperature below about 40 C., there being employed at least one mole of dinitrogen tetroxide for each mole of propylene, reacting the resultant reactant products with at least one mole of nitric acid for each mole of propylene employed, said nitric acid having an HNO concentration in excess of about 25 percent by weight, and recovering the lactic acid produced.

References Cited in the file of this patent UNITED STATES PATENTS 2,402,315 Crowder June 10, 1946 2,511,915 Himel June 20, 1950 2,525,353 Himel Oct. 10, 1950 FOREIGN PATENTS 742,053 Germany Nov. 22, 1943 62,760 Netherlands Apr. 15, 1949 OTHER REFERENCES Haitinger: Ann. Chim. (Liebig), 1 93 (1878), pp. 376-83. 

1. THE PROCESS WHICH COMPRISES CONTACTING PROPYLENE WITH AN OXIDIZING MEDIUM AT A TEMPERATURE BELOW ABOUT 40*C., SAID OXIDIZING MEDIUM CONTAINING AT LEAST ONE MOLE OF NITRIC ACID AND AT LEAST ONE MOLE OF DINITROGEN TETROXIDE FOR EACH MOLE OF PROPYLENE EMPLOYED, SAID NITRIC ACID HAVING AN HNO3 CONCENTRATION IN EXCESS OF ABOUT 25 PERCENT BY WEIGHT, SUBJECTING THE RESULTANT REACTION PRODUCTS TO HYDROLYSIS CONDITIONS, AND RECOVERING A PREPONDERANCE OF LACTIC ACID. 